The invention relates to three dimensional model building, and more particularly to methods and apparatus for creating three dimensional objects using active feedback.
A considerable number of methods and systems have previously been described for building three dimensional models by automated machines or processes. These can be categorized generally into two types of processes, subtractive processes and additive processes.
In subtractive model building processes, generally the process involves removal of material by some sort of tool, from an original block of material. Conventional machining of metals, plastics and other materials by machine tools has been automated for some time, and by such systems relatively complex three dimensional shapes can be generated from a computer program. In U.S. Pat. No. 4,238,840 (Swainson), three dimensional figures were described as formed in a medium having two active components by causing two radiation beams to intersect in the medium. The surface of a desired figure or shape was traced within the medium, then solvent was used to strip away excess medium material external to the generated shape or model. The Swainson system used a computer to feed information to the model creating tools, i.e. lasers, and in this sense the patent is representative of other prior methods wherein stored computer programs were used for making three dimensional models based on stored information.
U.S. Pat. No. 3,635,625 (Voss) discloses an apparatus for carving a material in sheet form to produce a desired surface pattern. The patent is primarily concerned with carving surface patterns into carpeting, and discloses the use of carving fluids such as hot inert gas, hot air, steam or burning gas.
In the additive process for three dimensional model building, material is added or created or goes through a state change. This process is represented in several prior publications by the use of photo hardenable liquid materials cured and hardened by specified radiation, such as ultraviolet light. In Hull U.S. Pat. No. 4,575,330, three dimensional objects were described as generated by creating a cross-sectional pattern of the object to be formed at a selected surface of a fluid medium which can be hardened by radiation. The process of the Hull patent, controlled by a computer, was essentially two-dimensional, in that successive adjacent cross-sectional layers of the object were successively formed in a step-wise laminar buildup of the desired model. A stage or platform was moved, i.e. lowered in a liquid volume, while a writing head traced successive layers of the desired three dimensional shape at the surface of the liquid.
Somewhat similar processes were described in an article entitled "Automatic Method for Fabricating a Three-Dimensional Plastic Model With Photo-Hardening Polymer", by Hideo Kodama, Nagoya Municipal Research Institute, Rev. Sci. Instrum. 52(11), November 1981. The article described formation of an object in layered, stepped stages from the surface of a liquid bath of the photo-hardenable material, or alternatively from the bottom of the liquid volume. Light capable of curing the polymer was played onto the surface and the desired shape of a layer was created by using an appropriate mask; or an optical fiber was manipulated by an X-Y plotter to trace each layer in succession.
U.S. Pat. No. 3,974,248 disclosed, in the context of a thermoplastic sheet material, a system for determining or controlling the profile of a property of the sheet-like article. Monitoring of the properties was accomplished by means of electrical gauging signals, positioned across the width of a sheet of material advanced from a roll. Principally, the disclosure was concerned with the determination and control of the thickness profile of sheet materials formed by processes such as rolling, calendering and extrusion. The monitoring system disclosed in the patent could be used as feedback to apply corrective measures automatically to the manufacturing processes, to return the thickness profile to the desired specifications.
However, the Atkinson patent did not deal with formation of three dimensional models such as is concerned with the present invention, and the principles disclosed relative to thickness profiles of sheet materials would be of limited use in constructing relatively complex shapes in three dimensional models.
There has been a need for an accurate yet relatively straightforward system for producing three dimensional models, at reasonably good speed and at moderate cost. Those are objects of the present invention described below.